Internally finned tube



United, States Patent C INTERNALLY' TUBE Hugh L. Gaddis, Cleveland Heights; Glenn WZ Myers; North Ridgeville; and OralS. Welsh, El-'yria, liio,-as-- signors to Brown Fintube Company; Elyria; Ohio, a corporation of Ohio Original application September 18,, 1950; Serial. No. 185,418. Divided and this applicatibnMlayZfi, 1952', Serial No. 290,054-

6'Claims. (Cl. 13838) The invention of this application; which. is a division of. application Serial N0..-185,-418;o filed. September 18', 1950, for Tube With InternalFinsand Method of Mak ing Samef has to do with internally'finned tubes.

Tubes with internal finsi to provide extended surface area are highly useful in many installations, for. example, for use as fire tubes in domestic heating boilers Because' of the expense of. manufacture of sucl'i'v tubes and in some instances the; unsatisfactory characteristics of the completed tubes, internally finned tubesiheretofore' have not had extended use. The present inventionhas' for its general objects the provision offinternally finned tubes in which the difficulties With previousfitypesl of tubes are overcome.

Briefly, internally finned heat'exchange" tubesare: provided by assembling a plurality of: channelf section fin members on a polygonal supporting mernber having anumber of sides equal to the number: ofichannel: mentbers; the base portions of the. channel members engage; the sides of the polygonal supportingzmember and the edges of the base. portions: of the channels on adjacentsides of the supporting member? are in contact with each other. The assembly so produced is then intro duced into a tube by pressing. or driving the partsito=- gether with the outer edges of: the fins firmlyrenga'ging the inner surface of the tube. Thenthe supporting member isremoved leavingthe: channelimemberssup ported within the tube with thevouter edges'of the fins' held against the innersurface of the tube: solely'by the engagement between the ed'gesof. the" base' portions of adjacent channels. The assemblyfis'completed bybraz ing the fin members to' the tube.

This'produces an internally'finn'edztube in:which the fins are bonded to the tube'by: alloy bonds' of g'ood h'eat conducting characteristics and in. which there are no supporting members for the fins other than the'tube. The central portion of the tube remains open-for. the passage offluid therethrough' and the finned portions of the channels are spacedapart by tlie'widthiof' the -bases of the channels; hence, there is'nol' undue-crowding of the inner portionsof the finstand pre'ssure drop through the tube is held me minimum.

Referring now to the drawings, Figure 1- isaa;pers'pec'- tive. view of a preferred form ofl an internally finned tube made ucording-v to: our invention;. Figure- 2- a perspective showing the assembly of fin members and a supporting her prior to introductioninto the tube; Figure 3 is adetail'of orient the channeisg'and Figure 4 illustrates the step of insertion of the'assembly. of fin members and supporting bar into thertube.

An internally finned tube embodying" our invention preferably comprises a tube and:a plurality of.channel' section fin members 11 disposed within the"- tube. Each channel section fin member comprises a base portion 12 and fin portions 13. Preferably, each fin portion terminates inalongitudinally extending; laterally turned flange" 14-whiehconstitutes the' outer edge of the fin and which in the completed tube engages and is bonded to-theinterior surface of. the tube 10.

The-flanges 14- are provided: for the reason that the construction of the tube requires that the dimension indicated by a in" Figure 3- between the bottom of the base portion 12 andthetopof flanges 14 be held accurately to rather close tolerances; 14 the dimension a can be determined accurately'by the construction of the rolls which bend the strip material utilized to make the channels into the desired channel section and slight variations in the Width of the original strip-willnot affect this dimension; thus the dimension n can beheld within close tolerances. If such flanges are notprovided it is necessaryto maintain the width of thestrip with ahigh degree of accuracy and to center the rolls accurately with respecttothe strip to insure that-the fin portions willbe of: equal anduniform length. Even under otherwise favorable conditions, camber in thestrip maygive rise to' unequalfin portions.

The proportions of the channel section-members 11 are selected so that when the desired number of channels aresecured" within the. tube asshown in Figure 1 the base portions l2of-. the several? channels define a polygonal opening 15- atthe center of the tube. In the example shownthe opening is hexagonal; six channel members being. employed. Those skilled in the art, however, will appreciate that greater or lesser numbers of. channel members can be utilized if desired. The width of thebase-portionslZ-is such that the edges of thebase portions where the fin portions extend therefrom abut the-edges" of the base portions of adjacent channels as indicated at. 16.- This engagement of the edges-of the bases firmly supportsthe channels against external forces and-thus thechannelsreinforce'the tube against. external. pressures; 1

In.- the completed tube the'flanges 14' are preferably bonded to the inner"v surface of the tube by an alloy bond in orderto-obtain good heat transfer. The contactingedgesof the base portions may be b'onded by a similar bond in order to improve themechanical strength of the asssembly but such bonding is not essential. When ferrous tubes are employed; copper may be utilized as the-bondingmateriah With non-ferrous metals suitable brazing. alloys 0r= solders maybe employed dependingupon-the service to which the tube isto' be put.

Inproducingthe tube shown in Figure l, the first step ism-assemble the desired number of channel members (six in-thepresentexamplelwith a supportingrod 18 which: is in the form-of a-polygon'having a number of sides equal to the: numberof. channel members and with the faces 19' of the rod'substantially. equal to the width-of.the bases of.the channels; Such an assembly isshown irrFigure-Z from which-it will' be seenthat- V Thechannel members-are temporarilyheld on the rod 18 by. any convenient: means such as encircling wires or bands-or? small areas of. solder of low melting temperature. With-the channels-so held on the rodj the'a'ssem blyof Figure-2"is then introduced into-tliextube 10 as shown'inFigure 41 This operationmaybe'carried out- After! the fins-a're 'properly' positioned within the tube the sup orting: rod 18 is withdrawn from the assembl'j-leaving th'e'fin' membersin the tube With-thefla'ngesl t sup'ported firmly'in' engagement withtiie inner'snrface of the ttrbebythe engagement between channels along the the e'dgesof' theba'se portions of the lines 16? In order to complete the assembly, bonding metal is By providing flangesportion.

supplied to the contacting areas of the parts that are to be bonded together. tion is employed, copper paste composed of finely divided copper or copper'oxide powder in a liquid or paste vehicle is introduced into the tube andcaused to fiow so that a fillet of paste is provided ateach contact point between the flanges 14 and the tube and between the edges of the bases 'of adjacent channels if it is desired to bond these edges together. The tube is then passed through a brazing furnace having a reducing atmosphere such as provided by hydrogen or a cracked hydrocarbon gas and raised to a temperature of about 2100 degrees ically strong bond having excellent heat transfer characteiistics. The copper bond is 'able to withstand the temperatures ordinarily encountered in domestic fire tube, boilers and in similar situations. Wherelower surface temperatures are contemplated; it is possible to use brazing alloys and solders of lower melting points as the bonding medium.

From the foregoing description of a preferred form of our invention it will be seen that we have provided efiicient heat exchange tubes having internal fins which are capable of being manufactured with comparatively simple equipment and at reasonable cost. Because the channel section members are self supporting by reason of their engagement with each other, no central support is required for these members in the completed tube; hence, the supporting bar 18 can be used repeatedly in manufacturing tubes, and the elimination of a supporting member in the completed tube results in a reduction in cost and in a more eificient structure from the standopen channel metal fin members extending longitudinally within said tube, each having a pair of fin portions and a base, the outer edges of said fins being bonded to circumferentially spaced zones on the inner surface of the tube, the inner surface of the tube being exposed between said zones, said fin portions extending substantially radially inward therefrom, each edge of the base of each' channel member being in contact with an edge of the base of an adjacent channel'member to provide a self-supporting, hollow center structure, said channel members being in contact with each other only at said edges, there being longitudinal passages on both sides of each fin portion.

2. An internally finned heat exchanger tube comprising a metal tube and a plurality of separately formed metal fin members extending longitudinally within said tube, each having a fin portion and a base, said fin portions being bonded to circumferentially spaced zones on the inner surface of the tube, the inner surface of the tube being exposed between said zones, said fin portions extending substantially radially inward therefrom, each edge of the base of each fin member being in contact with and bonded to an edge of the base of an adjacent fin member to provide a self-supporting, hollow center structure without internal support, said fin members being in contact with each other only at said edges, there being longitudinal passageways on both sides of each fin Where a copper brazing. operas,v

" 3. An internally finned heat exchanger tube comprising a metal tube and aplurality of separately formed open channel metal fin members extending longitudinally within said tube, each having a'pair of fin portions and a base, the outer edges .of said fin portions being bonded to the interior surface .of-th'eitube, said fin portions extending substantially radially inward therefrom, each edge of the base of each channel member being in con tact with and bonded to an edge of the base of anadjacent channel member to provide a self-supporting, hollow center structure without internal support, said channel members being in contact with each other only at said edges, there being longitudinal passageways between adjacent channel member's.

4. An internally finned heat exchanger tube comprising a tube of ferrous material and a plurality of separately formed open channel fin members of ferrous material extending longitudinally within said tube, each having a pair of fin portionsand a base, the outer edges of'said fin portions being copper-brazed to the interior surface of the tube, said fin portions extending substantially radially inward therefrom, each edge of the base of each channel member being in contact with and copper-brazed to an edge of the base of an adjacent channel member to provide a hollow, self-supporting center structure'with out internal support, said channel members being in I contact with each other only at said edges, there being longitudinal passageways between adjacent channel members.

5. An internally finned heat exchanger tube comprising a metal tube and a plurality of separately formed open channel metal fin members extending longitudinally within said tube, each having a pair of fin portions and a base, said fin portions having'longitudinal flanges at the outer edges thereof, .said flanges being bonded to the interior surfaceof the tube, and said flangesengaging circumferentially spaced'zones on the inner surface of the tube, the inner surface of the tube being exposed between said zones, said fin portions extending substantially radially inward therefrom, each edge of the base of each channel member being in'contact with an edge of the base of an adjacent channel member to provide a self-supporting, hollow center structure, said channel members being in contact with each other only at said edges, ,there being longitudinal passageways between adjacent channel members.

6. An internally finned heat exchanger tube compris- 7 ing a tubeof ferrous material and a plurality of separately formed open channel fin members of ferrous material, each having a pair of fin portions and a base, said fin portions having longitudinal flanges at' the outer edges thereof, said flanges being copper-brazed to the interior surface of the tube, and said flanges engaging circumferentially spaced zones on the inner surface of the tube, the inner surfaceof the tube being exposed between said zones, said fin portions extending substantially radially inward therefrom, each edge of the base of each channel member being in contact with and copper-brazed to an edge of the base of an adjacent channel member to provide a self-supporting, hollow center structure without internal support, said channel members being in contact with each other only at said edges, there being longitudinal passageways on'both sides of each fin portion.

References Cited in the file of this patent UNITED STATES PATENTS 

